1. Field of the Invention
This invention relates to air-entraining water reducing agents for a cement composition suitable for addition to mortar and concrete, and, more specifically, to air-entraining water reducing agents for cement comprising a higher secondary alcohol oxyalkylene sulfate as an active ingredient.
2. Description of the Prior Art
Cement additives having air-entraining properties are used for improving the properties of mortar and concrete, and a variety of such additives are known. For example, salts of resin acid or modified products thereof, sulfated ester ammonium salts of higher primary alochols (or addition products thereof with ethylene oxide), alkylbenzenesulfonic acid salts, other synthetic detergents, salts of petroleum acids, fatty acids and proteinaceous substances, and organic salts of sulfonated hydrocarbons are known as air-entraining agents. Furthermore, ligninsulfonic acid salts or derivatives thereof, polynuclear aromatic sulfonic acid salts, polyalkylarylsulfonic acid salts such as sulfonated product of a condensate between creosote oil and formaldehyde, higher polyhydric alcohol salts such as polyoxyethylene alkyl ethers or polyol compounds, and hydroxycarboxylic acid salts are known as air-entraining water-reducing agents.
However, these air-entraining additives for cement are not entirely satisfactory with respect to the stability of the air bubbles in concrete, the effect of improving the workability of the concrete and the effect of reducing the amount of water required. For example, concrete containing the above-mentioned air-entraining agents or air-entraining water-reducing agents has poor water-entraining effect stability depending upon the temperature at which the concrete is mixed, or when fly ash or magnesium fluoro silicate is added to the concrete. Alternately, air bubbles in the concrete partly disappear at the time of transporting ready-mixed concrete in a concrete mixer truck, placing the concrete in the construction of skyscrapers, of dams or of the lining of tunnels, and transporting ready-mixed concrete by pumps. Consequently, this markedly reduces the workability of the concrete and results in a reduced operation efficiency. Furthermore, the disappearance of air bubbles results in the inability of the set concrete to attain the desired durability to freezing and thawing.
Another purpose of adding an air-entraining water-reducing agent to concrete is to disperse the cement particles in water at the time of mixing with a minimum amount of water being required, and to obtain the desired workability of the concrete, and further, to increase the strength of the cured concrete by an amount corresponding to the decrease in the unit amount of the water. Concretes containing the above-mentioned air-entraining water-reducing agents have fairly increased strengths initially as a result of the decrease in the unit amount of water, but their strengths at later stages are not entirely satisfactory and in some cases, the strengths are even lower than the strengths attainable without the addition of the air-entraining water-reducing agents.
In addition, the properties of concretes containing air-entraining agents, such as workability, setting time and strength, tend to be affected by the amounts of the additives, and the differences in chemical and physical properties of the cement and aggregate, and therefore, it is difficult to obtain concretes containing air-entraining agents and having stable properties.